Detection Methods And Replacement Of Capacitors

    Common faults of electrolytic capacitors include reduction in capacitance, disappearance of capacitance, breakdown, short circuit and leakage. The change in capacitance is caused by the gradual drying up of the electrolyte inside the electrolytic capacitor during use or placement, while breakdown and leakage.

    It is generally caused by the applied voltage being too high or the quality itself being poor. To judge the quality of electrolytic capacitors, the electrical barrier of a multimeter is generally used to measure it. 

    The specific method is: short-circuit the two pins of the capacitor to discharge, and use the black test lead of the multimeter to touch the positive electrode of the electrolytic capacitor. The red test lead contacts the negative electrode (for an analog multimeter, the test leads intermodulate when measuring with a digital multimeter). 

    Normally, the test needle should first swing in the direction of small resistance, and then gradually return to infinity. The greater the swing amplitude of the watch hand or the slower the return speed, the greater the capacitance of the capacitor, and vice versa, the smaller the capacitance of the capacitor. 

    If the pointer of the meter stops changing somewhere in the middle, it means that the capacitor is leaking. If the resistance indication value is very small or zero, it means that the capacitor has broken down and short-circuited. Because the battery voltage used by a multimeter is generally very low, it is more accurate when measuring capacitors with low withstand voltage. When the capacitor has a higher withstand voltage, although the measurement is normal, leakage or breakdown may occur when high voltage is added. .

Replacement of capacitors: It is required that the withstand voltage cannot be lower than the original one. It does not matter if the capacitance can deviate a little, but it also depends on the actual application circuit. Some circuits have strict requirements on the capacitance of the capacitor and must be replaced with a capacitor of the same capacitance.

Notice:

① The electrolytic capacitor is leaking, bulging, or deformed;

②The surface of the chip capacitor must be free of damage. If there is damage, it is considered bad (it cannot be measured with a multimeter, and its quality can only be judged by the replacement method);

③SMD capacitors for parallel ports and PS/2 ports are most susceptible to damage;

④The capacitor (not grounded) next to the power IC must not be replaced randomly;

⑤ Ungrounded capacitors around the sound card cannot be replaced randomly.

When replacing a capacitor, the capacitance, voltage resistance, and temperature resistance cannot be lower than the original parameters, but they cannot be too high, preferably higher than 20%. Some chip capacitors do not have marked parameters, so you can only replace them with ones of similar size and color.

Also look for a replacement with the same location on another motherboard. For example, if the coupling capacitor next to the PCI-E slot is broken, you can replace it with the capacitor next to the PCI-E slot on another scrapped motherboard.

For a good capacitor, the display result is as shown in Figure 4-41.

Figure 4-41 Capacitance of normal capacitor In Figure 4-41, it is normal for the capacitance of the capacitor to be OL. A bad capacitor is shown in Figure 4-42.

                             Figure 4-42 Capacitance of a bad capacitor

In Figure 4-42, the capacitance is 0, indicating that the capacitor has been short-circuited.